SDA2b life support

[jcandy]

I am trying to revive my uncle's SDA2Bs that suffer from (at least) the blown-tweeter problem. These speakers have great sentimental value: in fact, I drove them home myself in 1990, in a 1986 Honda Civic hatchback. I lost contact with him in the period 2002-2010, but recently he had a stroke :(. Now I am helping him to sell some items, and since I am a DIY audio fanatic, I offered to deal with the complete setup (also includes the high-end NAD pre-amp-tuner-cd from that era). The entire system was ridiculously expensive when purchased in August 1990 (seems like yesterday ...), and oddly enough, hasn't really been used for about 10 years. My uncle doesn't really like music!

Over the years, I believe two sets of replacement tweeters were ordered, but all tweeters he can locate are *dead*. I tested a random spare tweeter and this produced a roughly correct SPL, so I know there is a signal to the tweeters. The inner 6.5 driver is making NO sound, but I suspect this is because I don't have the SDA interconnect.

What should I do? Attempt to locate replacement tweeters, upgrade the crossover (I am comfortable with that), just sell them as-is, what

[helipilotdoug]

Welcome to Club Polk. :) Those 2b's are very good speakers, and can be fixed very easily. Polk Audio sells replacement tweeters for $48 each plus free shipping for Club Polk members. There are many tweaks and upgrades that can be done to them, which will make them outstanding speakers. The interconnect cable is very important, so try to find it. If you can't, you can find one, make one yourself, or get with ben62670 who makes them. Unless you really need to sell them, I'd keep them and do the upgrades below.

Here are some links that I have found very helpful and great reading. I'm sure there are more.

Most of the tweaks are covered in this great post started by TOOLFORLIFEFAN:
http://www.polkaudio.com/forums/showthread.php?t=97719

And another thread by nspindel that covers several tweaks:
http://www.polkaudio.com/forums/showthread.php?t=62106

Mortite:
http://www.polkaudio.com/forums/showthread.php?t=74524

Dynamat:
http://www.polkaudio.com/forums/showthread.php?t=52810

Hardware Rings:
http://www.polkaudio.com/forums/showthread.php?t=103241

SDA2B Crossover upgrade:
http://www.polkaudio.com/forums/showthread.php?t=87121

Hope this helps.
Doug

[inspiredsports]

Welcome to CP.

I have been down your exact path and will be glad to help as best I can.

I have TL'd 2B's (that I bought stock in 1987), an NAD 7600 receiver I bought the same day (7600 Receiver incorporate 1300 preamp, 4300 tuner and 2600 Amp in the same package). plus have owned and sold a 4300, and later purchased a 1700 preamp/tuner (incorporates 1300 and 4300) and a separate 2600A!

I've performed (with help) all mods possible on the 2B's, and all of my NAD components have been sent out for mods/caps/power upgrades within the past 12 months.

The gear in your photo can provide you with EXCEPTIONAL sound reproduction :)

Can you post images of the back with a closeup on the terminals / SDA interconnect socket?

[jcandy]

Here are some links that I have found very helpful and great reading. I'm sure there are more.
Thanks very much for the comprehensive reply! I appreciate it.

[jcandy]

I have TL'd 2B's (that I bought stock in 1987), an NAD 7600 receiver I bought the same day (7600 Receiver incorporate 1300 preamp, 4300 tuner and 2600 Amp in the same package). plus have owned and sold a 4300, and later purchased a 1700 preamp/tuner (incorporates 1300 and 4300) and a separate 2600A!
First of all, thanks so much for the speedy reply. Sadly, the CD player powers up but does not play, and the preamp has some contact problems when the tone controls are active.


Can you post images of the back with a closeup on the terminals / SDA interconnect socket?
Sure.

[inspiredsports]

Great, photos. You have the 1987 Pin/Blade model.

If you ever need to look at a schematic, go to http://www.polkaudio.com/forums/showthread.php?t=55888 and open up the SDA 2B 1987-pb Sch.pdf file.

[jcandy]

Status report: took one speaker apart and had a look at the internals and crossover. Yikes, what a MASSIVE air-core inductor -- 16mH! I suspect a proper replacement would be > $100.00, if somebody was willing to wind it for you. Someone on this forum, in describing a crossover tweak for the SDA2B, replaced this with a steel-laminate (SL) inductor. I am very suspicious of such a change, as the lower DCR of the SL inductor will alter the very-low-pass filter characteristics, perhaps for the worse, although I need to stare at the crossover schematic a little longer to make complete sense of the dimensional bit. Also, in the original crossover design, the huge magnetic field of this inductor will affect the other inductors. This was probably taken into account somehow in the original design. Has anyone seen FR plots for the unmodified and modified SDA2Bs? I wouldn't in a million years attempt to modify the crossover without such data. The SDA feature would be difficult to sort out in the measurement process, which is usually based on a mono MLS analysis.

That said, I pulled out the dead SL2000s and popped in a pair of Vifas I had lying around, and also built a temporary IC with some spare pin/spade connectors. The system sounded roughly correct, although bright (the Vifas are probably more efficient than the SL2000s). I didn't push the system hard, as cabinet leakage would muck up the bass response significantly.

Now I am re-gluing the side panels which had all but fallen off. I am a little afraid that the fit won't be super tight, but I'll know for sure tomorrow.

I guess the next step is to order a pair of the RDO-194 ...

[Joe08867]

Replacing the Air Core Inductor is really a waste of time. Replacing the caps is more the way to go.

The replacement RDO-194 is a very efficient speaker as well. If you decide to do the TL modification then you would want to replace the tweeter with the RDO-198. Considering your tweeters are shot I would vote you go that way.

[mmadden28]

^^^^ +1

Welcome to Club Polk

[Bobsama]

Replacing the Air Core Inductor is really a waste of time. Replacing the caps is more the way to go.

The replacement RDO-194 is a very efficient speaker as well. If you decide to do the TL modification then you would want to replace the tweeter with the RDO-198. Considering your tweeters are shot I would vote you go that way.

Though to add, iirc, you'll need to add resistance so that the RD0198's will play at the correct levels. Also take a few notes on where you set the speakers up. Placing them close to a wall reinforces bass response so you'll want to play around with them until you are happy. Also to note, the speakers are not to be toed in.

[mmadden28]

Though to add, iirc, you'll need to add resistance so that the RD0198's will play at the correct levels..

Correct-That is part of the TL mod.

[jcandy]

Replacing the Air Core Inductor is really a waste of time. Replacing the caps is more the way to go.
Yes, I can understand replacing the capacitors because of the tendency to degrade over time. Replacing the air-core inductor with steel-laminate could really be an *error*, since the two will differ significantly in DC resistance. Generally speaking, if you switch from air-core to SL in a low-pass filter, you will raise the level of the low-pass transfer function, accentuating the bass. Maybe this is the "bass slam" people spoke of :(

To put it another way, that massive air-core is a thing of beauty, one of the key components for the SDA effect, and will not degrade over time. I wouldn't mess with it.


The replacement RDO-194 is a very efficient speaker as well. If you decide to do the TL modification then you would want to replace the tweeter with the RDO-198. Considering your tweeters are shot I would vote you go that way.
Right. Maybe I just need to flip a coin! I really would prefer to leave the crossovers stock, as they appear to be functioning properly. The RDO-194 is a drop-in replacement as I understand it, and corrects the main fault of the SL2000, which was high-frequency peaking somewhere. It would be nice to see SPL traces for the SL2000, RDO-194 and 198 tweeters, otherwise its a bit like shooting in the dark.

[jcandy]

Correct-That is part of the TL mod.
Are there FR plots showing "before" and "after" the modification?

[inspiredsports]

. . . I really would prefer to leave the crossovers stock, as they appear to be functioning properly. The RDO-194 is a drop-in replacement as I understand it, and corrects the main fault of the SL2000, which was high-frequency peaking somewhere. It would be nice to see SPL traces for the SL2000, RDO-194 and 198 tweeters, otherwise its a bit like shooting in the dark.

RDO194-1's are a fine tweeter in their own right, but in my opinion, not as smooth and refined as the RDO198-1.

You could drop in the 194's without touching anything else, but then all you are doing is smoothing out the obnoxious (tiring) high frequency peak the SL2000's present. However, you would be missing much of the sound that was originally there when those now degraded 20 year old (and cheap) caps were new, plus listening to the noise even one cycle of protection imparted by the polyswitches.

In my humble opinion, just dropping in 194's won't give you much for your $100 investment.

At a minimum, the polyswitches should be replaced (or most including me would advise snipping and bypassing). But . . . snipping and bypassing requires adding back the .5 oms of resistance they imparted to the circuit, Now you need a higher impedance resistor (increase the 2.7 to 3.2). IF replacing, Polk will generally send them for a song.

What the heck, now that you're in that deep, it's easier to spend the same $48 on 198's and replace the caps too.

If you are keeping them stock, why not find 2 SL2000's for about $40 delivered and then you are economically back to 1990. (and can sell the SL's for the same $40 when you decide 198's are the right answer) :D

PS.: Remember, the SDA-2B "TL" mod was a Polk approved mod. Overall sound pressure levels with SL2000 and RDO198-1's, to my recollection, was very similar, but it has been a couple of years.

[jcandy]

RDO194-1's are a fine tweeter in their own right, but in my opinion, not as smooth and refined as the RDO198-1.
Please forgive my skepticism, but unless I see an FR plot showing the difference I would be afraid do it. What does smooth and refined mean in terms of frequency response, power response, and directivity? Once I get the speakers working I desperately want to do some far-field FR measurements. This will establish a sort of baseline performance. Maybe the RDO-194 just needs some minor response shaping or attenuation, which may be possible by just adding a series and shunt resistor (L-pad).

Um, sorry if I am coming across as a bit of a jerk here. I really do appreciate your feedback, information, etc :o


You could drop in the 194's without touching anything else, but then all you are doing is smoothing out the obnoxious (tiring) high frequency peak the SL2000's present.
Are you aware of any measurement which shows the location and magnitude of the peak?


However, you would be missing much of the sound that was originally there when those now degraded 20 year old (and cheap) caps were new
Yes, I am a little worried about degradation of the capacitors. This would be the main reason to make new crossovers.


In my humble opinion, just dropping in 194's won't give you much for your $100 investment.
Well, now I have no tweeters period (both originals are dead), so I will certainly get something! And I see people dropping ridiculous $$$ on "boutique" capacitors when simple Dayton/Bennic or Erse would be indistinguishable.

If I decide to modify the crossovers, what I would do is make new boards, leaving the original boards intact. I would only reuse the monster inductor. However, I would also mount the new boards on the bottom of the enclosure, rather than atop of the monster SDA inductor, so as to reduce the field interaction:

http://techtalk.parts-express.com/showthread.php?p=1500176

Cheers!

[inspiredsports]

I hope you don't think I'm being critical and I hope I didn't come across that way.

I will say that I used to be from Missouri (the "Show me" state :D) and I have absolutely learned now to trust my ears versus empirical testing which in my opinion provides only a hint as to what you will hear.

I spent a lot of time (and money) trying to "snip the dog's tail off an inch at a time". Then at some point I just started to trust the guys here, especially F1 who may come across differently than the genuine Polk guru that he is, and others too numerous to mention so this does not become a CP commercial.

I now have some of that "boutique" stuff, and I won't bore you with details. However, here we are talking about Sonicaps (http://www.soniccraft.com/sonicaps.htm) where you get 93-100% (an A grade on any curve) of what the boutiques offer for just a few dollars more than caps you mention.

I don't know if Face has some of the quantitative stuff you are asking for, but if not you should get his qualitative opinion. There a probably 4 dozen guys here who have been around the block with Polk who can tell you much more than I. But if anything, next time I ABSOLUTELY will go with the boutique stuff, because the Polk SDA-2B design sounds absolutely that good.

[jcandy]

Lately I have been using Erse ($7.47 for 20 uF) capacitors:

http://meniscusaudio.com/20uf-250v-p-369.html

This is almost a factor of 4 cheaper than the equivalent SoniCap. For the large values needed by the SDA2B, I would probably go with Solen:

http://meniscusaudio.com/20uf-400v-p-321.html
http://meniscusaudio.com/40uf-400v-p-326.html

which are only slightly more than the Erse.

[Joe08867]

I am a big fan of Sonicaps. For the price they are tops in my book.

To go back a little. The SL2000 tweeter has a harsh spot in the upper end of its range that is irritating at best and annoying to most. I am sure this has something to do with Age and design but I prefer the sound of the RDO194.

Now as far as the RDO198 is concerned the TL modification we talked about changes the resistance to match that tweeter and really opens up the sound of those speakers.

I would look at the capacitors like mini batteries. Would you use a battery that was 20 years old or would you replace it with a brand new one? I would replace it. Even if it worked it is nowhere near the efficiency they get nowadays and will almost guarantee the speakers work well for another 20 years.

[Joe08867]

I was searching some older posts and it looks like the peak would be at 13khz on the SL2000. It has been noted in most magazine tests of the speakers back in the day and is attributed to the SL2000.

The SL3000 fixed this issue later on, but it was never made available for the SDA2's. And should not be used unless you do the TL mod.

http://www.polkaudio.com/forums/attachment.php?attachmentid=5344&d=1093023963

[heiney9]

Lately I have been using Erse ($7.47 for 20 uF) capacitors:

http://meniscusaudio.com/20uf-250v-p-369.html

This is almost a factor of 4 cheaper than the equivalent SoniCap. For the large values needed by the SDA2B, I would probably go with Solen:

http://meniscusaudio.com/20uf-400v-p-321.html
http://meniscusaudio.com/40uf-400v-p-326.html

which are only slightly more than the Erse.

Except the Sonicaps are 7 times better sounding.

H9

[inspiredsports]

Except the Sonicaps are 7 times better sounding.

H9

+7 to that :D

[inspiredsports]

jcandy,

If you were to walk into a showroom (or find online deals) for brand new gear comparable to the stack of NAD's plus the SDA 2B's in the image in your first post, you would probably be laying out 6-7K.

Saving a few dollars on caps is admirable, but it does not do the system, especially the speakers justice.

But . . . I certainly do respect your desire to save money.

[inspiredsports]

Vintage SL2000's may be for sale here if pending sale fell through ... http://www.polkaudio.com/forums/showthread.php?t=105249 . . . and he's a very trustworthy Polkie if they are available

[jcandy]

Except the Sonicaps are 7 times better sounding.

H9
Really? When I am designing a crossover, how do I account for this dramatic variability in capacitors, other than by its capacitance? Let's assume we are talking about modern polypropylene capacitors. Is there a nonlinear shift in the capacitance or something?

It seems to me fiddling with inductors is probably worthwhile, since just rotating an inductor will change its inductance, as well as the inductance of all surrounding inductors. In designing my own speakers I tend to separate the woofer and tweeter filters so as to maximize inductor-inductor spacing. From this POV, the modified crossovers I see here, with hyper-expensive capacitors along side poorly-oriented inductors is telling.

I am ready and willing to believe there are audible differences between capacitors as soon as someone can "show me the measurements" as it were. In the meantime, its Erse/Dayton all the way.

[F1nut]

As long as you are stuck in the show me the measurements state of mind, audio nirvana will never be obtained.

Anyway, this is a great read. http://www.humblehomemadehifi.com/Cap.html

[jcandy]

jcandy,

If you were to walk into a showroom (or find online deals) for brand new gear comparable to the stack of NAD's plus the SDA 2B's in the image in your first post, you would probably be laying out 6-7K.

Saving a few dollars on caps is admirable, but it does not do the system, especially the speakers justice.

But . . . I certainly do respect your desire to save money.
Its not really about saving money, its more about not throwing it away. There's a significant difference. You see, when I look at (and in) the SDA2Bs, I see a very clever, innovative speaker, but with some problems that cannot be solved with the use of boutique capacitors, such as: inadequate bracing, poor inductor placement, 90 degree baffle edges, large tweeter-mid CTC spacing (which gives rise to lobing). The crossover on the tweeter is only second order which probably does not provide optimal power handling (obviously!). Measurement may uncover further problems. For example, its not clear what the distortion numbers are. This is a critical consideration when starting a new design, and also cannot be cured in the crossover. Instead, you have to start with a low-distortion driver like this one:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=296-602

This will sound more natural/correct in the critical midrange than the Polk MW6503. Moreover, I do not understand the SDA crossover well enough at the moment to improve it. With something like a monitor 5/7/10 it would be easier.

Anyhow, I now have them up and running with the RDO-194s I picked up directly from the Polk Warehouse in Vista (just north of me). They sound very good (I have other "vintage" speakers from the 90s that sound horrific) but I can tell right away that the FR is not flat. I want to do some measurements to verify this, but have to figure out how to manage that with the SDA effect.

[F1nut]

You see, when I look at (and in) the SDA2Bs, I see a very clever, innovative speaker, but with some problems that cannot be solved with the use of boutique capacitors, such as: inadequate bracing, poor inductor placement, 90 degree baffle edges, large tweeter-mid CTC spacing (which gives rise to lobing). The crossover on the tweeter is only second order which probably does not provide optimal power handling (obviously!). Measurement may uncover further problems. For example, its not clear what the distortion numbers are. This is a critical consideration when starting a new design, and also cannot be cured in the crossover. Instead, you have to start with a low-distortion driver like this one:


You couldn't be more wrong. TL'd 2B's with better crossover components sound absolutely nothing like what you are hearing now. Add Larry's rings and as Russman says, you'll **** your flat hat.

[jcandy]

As long as you are stuck in the show me the measurements state of mind, audio nirvana will never be obtained.

Anyway, this is a great read. http://www.humblehomemadehifi.com/Cap.html
Yes I've seen that. I won't tell my wife, though. She's Dutch and wouldn't tolerate such subjectivity from a fellow countryman :)

I honestly doubt there is any significant improvement to be had over an Erse or Dayton poly.

[jcandy]

You couldn't be more wrong. TL'd 2B's with better crossover components sound absolutely nothing like what you are hearing now. Add Larry's rings and as Russman says, you'll **** your flat hat.
Does somebody have a measurement of the original versus the modified 2B? Seriously guys :mad:

Here is a measurement of what I just A/B tested the SDA2Bs against to verify that they do not have a flat frequency response.

[TrashyTrucker]

...

Anyway, this is a great read. http://www.humblehomemadehifi.com/Cap.html

F1nut,
That was a very good read! Thanks for sharing that with us. BTW if this guy DOES NOT want to change his uncles stock sda's, (may have sentimental reasons) then thats on him. I know I have had my SDA SRS 3.1's since the 90's and by all of you guy's testimonies, I will doing the other upgrades real soon.(the RDO198's worked well after breakin) I almost cant wait to recieve my packages in the mail! After that I will get started and soon begin the tedious task of breaking in the Sonicaps by playing hours and hours of music. :eek: JK, LOL :D cant wait!

Matt

[F1nut]

Why are you obsessed with a flat frequency response? It is not the end all that some think it is. I recall one of the better speaker designers mentioning that he built, with the help of test equipment and modeling programs, a speaker with a perfectly flat frequency response. He stated that it sounded like ****.

[jcandy]

Why are you obsessed with a flat frequency response? It is not the end all that some think it is. I recall one of the better speaker designers mentioning that he built, with the help of test equipment and modeling programs, a speaker with a perfectly flat frequency response. He stated that it sounded like ****.
Was this before he earned the reputation as one of the better designers?

I am not obsessed with a flat response, I am obsessed with facts. The frequency-response curve provides an important yardstick. The polar response, and the power response are also critically important depending on application. If we were talking about a center channel I'd have asked for polar response plot by now. Some people think the phase-response is also important, but in fact studies demonstrate that people are not sensitive to it. If you have a very reflective room, for example, what the flat FR curve tell me is that the speaker is probably going to sound bright unless you're over 50 and went to lots of Ted Nugent concerts in the 70s. My listening room is not very reflective so a flat SPL sounds good.

So, what I would do if I designed an improved crossover is offer a version with flat anechoic response, with instruction on how to progressively slope the tweeter response downward to suit the room characteristics by making simple changes to the shunt/series resistances.

[mmadden28]

Are there FR plots showing "before" and "after" the modification?

If I understand correctly, the 'TL' mod was a Polk Engineered design change which was applied to other models with the same crossover design-this wasn't something everybody just did.

Suggestions were made to you on what is generally accepted as the best sounding revision and since you had to buy new tweeters anyway it was suggested that you get the RD0-198s which would be the same cost as new RD0-194s and the only other addition is a 5.8µF cap (choose your poison).
All the other upgrades/improvements are simply recommendations for additional improvements that's all. Many still have their 2B's stock and love them.

You came here asking for advice as to what to do next, then you rebut with engineering this and that. So be it if you want them to remain stock, no need to be demanding FR plots and all that from the people trying to help you out based on what their ears hear. Sheesh.

[mmadden28]

Does somebody have a measurement of the original versus the modified 2B? Seriously guys :mad:

Here is a measurement of what I just A/B tested the SDA2Bs against to verify that they do not have a flat frequency response.

Did you perform that measurement in an anechoic chamber?

[jcandy]

If I understand correctly, the 'TL' mod was a Polk Engineered design change which was applied to other models with the same crossover design-this wasn't something everybody just did.

Suggestions were made to you on what is generally accepted as the best sounding revision and since you had to buy new tweeters anyway it was suggested that you get the RD0-198s which would be the same cost as new RD0-194s and the only other addition is a 5.8µF cap (choose your poison).
All the other upgrades/improvements are simply recommendations for additional improvements that's all. Many still have their 2B's stock and love them.

You came here asking for advice as to what to do next, then you rebut with engineering this and that. So be it if you want them to remain stock, no need to be demanding FR plots and all that from the people trying to help you out based on what their ears hear. Sheesh.
I appreciate the help and suggestions. I think I have rebutted only the boutique capacitor assertions (Sonicaps are 7 times better!), which seem implausible. Maybe its wasn't clear, but these are not my speakers, they belong to my uncle who's had a stroke and must sell them. For this reason I am not anxious to hack up the present crossover.

On the other hand, I've learned alot about the SDA series in the last few days and might acquire my own pair (for ethical reasons I don't want to keep these ones). In that case I'd consider more invasive modifications.

Thanks to those who offered advice. I really do appreciate it.

[jcandy]

Did you perform that measurement in an anechoic chamber?
Good question. Its quasi-anechoic. First, one measures the far-field response. The software applies a time window (smaller than the time for the first reflection to reach the microphone) to the MLS impulse to eliminate the effect of reflection, but limiting the validity of the data to about f > 300Hz. Then, the near-field responses of the woofer and port (or passive radiator) are taken and summed to get the complete near-field response. The near-field response is corrected by a numerical cabinet diffraction calculation to convert it to a far-field response (this is the one bit that could be subject to error, but turns out to be very accurate for typical MT and other speakers). Then, the near-field is spliced to the far-field at some joining frequency, usually about 400Hz. If the diffraction calculation was accurate then curves should overlap over a wide region, and if it does overlap you indeed trust that it was. In this case the overlap was great.

[inspiredsports]

I appreciate the help and suggestions. I think I have rebutted only the boutique capacitor assertions (Sonicaps are 7 times better!), which seem implausible. Maybe its wasn't clear, but these are not my speakers, they belong to my uncle who's had a stroke and must sell them. For this reason I am not anxious to hack up the present crossover.

On the other hand, I've learned alot about the SDA series in the last few days and might acquire my own pair (for ethical reasons I don't want to keep these ones). In that case I'd consider more invasive modifications.

Thanks to those who offered advice. I really do appreciate it.

OK, now I'm really missing something here.

If you are simply helping your uncle sell them, why not pick up 2 used SL2000's for $40 as I suggested a day or so ago, slap them in, and get them listed on eBay?

You won't improve your chances of selling them, or sell them for more money by modding them with cheap caps. And I certainly can't see why you are so argumentative and insistent about seeing frequency response curves for tweeters you would be putting in these for resale.

And they have immense sentimental value to you, yet you don't feel you can't keep them for ethical reasons?

So at any rate, you've got me really confused.

[heiney9]

Its not really about saving money, its more about not throwing it away. There's a significant difference. You see, when I look at (and in) the SDA2Bs, I see a very clever, innovative speaker, but with some problems that cannot be solved with the use of boutique capacitors, such as: inadequate bracing, poor inductor placement, 90 degree baffle edges, large tweeter-mid CTC spacing (which gives rise to lobing). The crossover on the tweeter is only second order which probably does not provide optimal power handling (obviously!). Measurement may uncover further problems. For example, its not clear what the distortion numbers are. This is a critical consideration when starting a new design, and also cannot be cured in the crossover. Instead, you have to start with a low-distortion driver like this one:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=296-602

This will sound more natural/correct in the critical midrange than the Polk MW6503. Moreover, I do not understand the SDA crossover well enough at the moment to improve it. With something like a monitor 5/7/10 it would be easier.

Anyhow, I now have them up and running with the RDO-194s I picked up directly from the Polk Warehouse in Vista (just north of me). They sound very good (I have other "vintage" speakers from the 90s that sound horrific) but I can tell right away that the FR is not flat. I want to do some measurements to verify this, but have to figure out how to manage that with the SDA effect.

Well apparently you know a WHOLE lot more about SDA's than Matt Polk and the engineers that conceived, built, tested and manufactured these speakers. :rolleyes::rolleyes:. Many if not all of the upgrades that have been done over the years have been suggested or discussed with Matt Polk and others close the SDA product at Polk and passed on, so it's not like all these suggestions are just wild hit and miss things.

For a more technical analysis I suggest you read these two articles and head to the library and read the "original" SDA white paper in the June 1984 Audio Magazine.

http://www.polksda.com/sda1creview.shtml

http://www.polksda.com/srsreview.shtml

Incorporating the newer silk dome RD0 tweeter gets rid of the steep resonant peak at about 13kHz the original sl2000 exhibits. There has been a discussion from Matt Polk about inductors in the SDA's so search for it. Additionally the SDA's can handle lots of power, where most people have issues is when they under power them. In fact if you read the test articles you'll see the 1C's could have taekn more power except the amp they were using at the time ran out of power before the speaker distorted around 800 watts give or take depending on the frequency. They are also flat +/- 5dB 20Hz - 18Khz if those measurements are important to you.

H9

[jcandy]

OK, now I'm really missing something here.

If you are simply helping your uncle sell them, why not pick up 2 used SL2000's for $40 as I suggested a day or so ago, slap them in, and get them listed on eBay?
Since the RDO-194 was a drop-in replacement and cures some of the SL2000s problems, that made the most sense to me. Replacing the tweeters with the "best" replacement part is not invasive. Since I live relatively close to the Polk warehouse, it was fast and easy for me to just run by and get them. Now the RDO-194s are in and work well. They are excellent speakers.


You won't improve your chances of selling them, or sell them for more money by modding them with cheap caps. And I certainly can't see why you are so argumentative and insistent about seeing frequency response curves for tweeters you would be putting in these for resale.
I am intrigued by these speakers, and they still do hold great sentimental value. I think in the future I would like to try to design a modified crossover for an SDA (on the other hand, a monitor 10 would be easier). And to answer your question in a general way, I just want to know the facts.


And they have immense sentimental value to you, yet you don't feel you can't keep them for ethical reasons
It would look like I'm freeloading! I said I would fix them (they were DoA with side panels off all fallen off) and sell them, and that's what I'll do. Because they have sentimental value I want to sell them to someone who will treat them well. I said I'd sell all that NAD gear, so I have to do that too, but I'm wasting too much time here! Honestly, I've learned alot in the last few days even if it seems I'm just a s--t disturber.


So at any rate, you've got me really confused.
Sorry for that. I've kind of got people jumping all over me by now.

[jcandy]

Well apparently you know a WHOLE lot more about SDA's than Matt Polk and the engineers that conceived, built, tested and manufactured these speakers. :rolleyes::rolleyes:.
When did I say or imply that? I am sure Polk would have done various things differently (bracing for example) had cost not been an issue. Slamming all the inductors together on one board, or omitting complex internal bracing, is something that starts to become very efficient/attractive in a mass-produced speaker, but its not something you need to do if you are building your own, or if cost is no object. Here's an example of a speaker that starts with spectacular drivers (the woofer is hand-made in the USA, the mid in Italy, and the tweeter in Denmark) and uses an enclosure that could withstand a nuclear blast:

http://www.aespeakers.com/phpbb2/viewtopic.php?t=1702

Nearly all of the (numerous) crossover components, however, are Dayton, which on this forum are apparently worse than garbage.


Many if not all of the upgrades that have been done over the years have been suggested or discussed with Matt Polk and others close the SDA product at Polk and passed on, so it's not like all these suggestions are just wild hit and miss things.
I believe that many of the upgrades are probably sound. But I have given examples of the more problematic information, like replacing the air-core inductor with an SL, or believing that changing a very good poly capacitor with another very good poly capacitor will "open up the soundstage". I would need to see real proof of that before I could believe it.

[heiney9]

I believe that many of the upgrades are probably sound. But I have given examples of the more problematic information, like replacing the air-core inductor with an SL, or believing that changing a very good poly capacitor with another very good poly capacitor will "open up the soundstage". I would need to see real proof of that before I could believe it.

Well, therein lies your problem, unless your ears can see. There is a very, very interesting discussion about inductors in SDA's from Matt Polk himself explaining inductors in SDA's. You could search for it if you are really interested in finding the proper answer.

Actually since i assumed you wouldn't bother to look for Matt and Stu's response I found it for you. This is specifically about the inductors in a pair of SDA SRS's, but I'm sure you can extrapolate the info to other model SDA's.

http://www.polkaudio.com/forums/showpost.php?p=1365585&postcount=5

[heiney9]

Here's one entire thread on SDA inductors

http://www.polkaudio.com/forums/showthread.php?t=103052&highlight=inductor

[jcandy]

Well, therein lies your problem, unless your ears can see. There is a very, very interesting discussion about inductors in SDA's from Matt Polk himself explaining inductors in SDA's. You could search for it if you are really interested in finding the proper answer.

Actually since i assumed you wouldn't bother to look for Matt and Stu's response I found it for you. This is specifically about the inductors in a pair of SDA SRS's, but I'm sure you can extrapolate the info to other model SDA's.

http://www.polkaudio.com/forums/showpost.php?p=1365585&postcount=5
Thanks for sending me the link. I did look for this but couldn't find it. Both these guys know exactly what they're talking about ;) Its also quite consistent, technically, with what I've been saying. One tricky point is related to the inductor DCR and bass response. Here's what I said earlier:

Yes, I can understand replacing the capacitors because of the tendency to degrade over time. Replacing the air-core inductor with steel-laminate could really be an *error*, since the two will differ significantly in DC resistance. Generally speaking, if you switch from air-core to SL in a low-pass filter, you will raise the level of the low-pass transfer function, accentuating the bass. Maybe this is the "bass slam" people spoke of
and here is what Polk said,

Decreasing the DC resistance will definitely improve the bass response of the system both qualitatively and quantitatively. However, before you rush out to buy those Hi-Q replacement inductors be aware of some concerns.

However, in this case, improve means "raise". Generally speaking, shaping the bass response is an application-dependent exercise. What designers normally do is provide options for bass tuning in connection with intended application. If you are placing speakers close to the wall and excite room modes sufficiently, or if you are using them for near-field monitors, there is not much need for baffle-step compensation (BSC), although there may be a need for tweeter attenuation in a design with a uniform power response. But if you have an open room you might want up to +6dB of BSC. In my most recent design I used two inductor stages to ensure a full +6db of BSC as well as a perfectly flat SPL. I also like the sound of full-BSC designs, which are equivalent to flat anechoic far-field designs.

I guess the point is that just swapping out components is a hit-and-miss approach, which is awfully time-consuming. For this reason, it is extremely important to have an SPL trace of the stock SDA2B before attempting any modifications.

[sda2mike]

[QUOTE=jcandy;1418066]

Nearly all of the (numerous) crossover components, however, are Dayton, which on this forum are apparently worse than garbage.


huh?? my xovers were done to TL standards by the highly-respected ben..he's done lot's of member's xovers...guess what? my xovers have 1 dayton each! the rest are sonicaps. i highly doubt that ben would install something less than garbage.

you might want to stop thinking about graphs and charts and articles and just listen...to the music AND the guys here who know wtf they're talking about.

mike

[jcandy]

Here's one entire thread on SDA inductors

http://www.polkaudio.com/forums/showthread.php?t=103052&highlight=inductor

After reading this over and over, Polk really makes it seem as though the reduced DCR will give unequivocally better low-frequency response because it removes the (unwanted) SDA effect (although the the speaker will have dangerously low impedance). I find it hard to believe. But, I guess its possible. Interesting.

Thanks for the links.

[jcandy]

huh?? my xovers were done to TL standards by the highly-respected ben..he's done lot's of member's xovers...guess what? my xovers have 1 dayton each! the rest are sonicaps. i highly doubt that ben would install something less than garbage.
I assure you the Daytons (which are Bennics) are excellent.


you might want to stop thinking about graphs and charts and articles and just listen...to the music AND the guys here who know wtf they're talking about.
But I can't stop thinking about them! I will post measurements of the SDA2Bs as soon as I can. Should be an eye-opener!

[heiney9]

I assure you the Daytons (which are Bennics) are excellent.

They are OK, certainly not garbage, but certainly not anything above average.

H9

[inspiredsports]

They are OK, certainly not garbage, but certainly not anything above average.

H9

Great caps don't seem to be as critical in the low pass section, but I can attest that Sonicaps or better DO make a difference up top.

[F1nut]

I think I have rebutted only the boutique capacitor assertions (Sonicaps are 7 times better!), which seem implausible.

H9 was being conservative, IMO. I'd say the Sonicaps are at least 10 times better.

[inspiredsports]

I'm curious about what you did with your uncle's SDA-2B's, (especially with all that's transpired since several other members and I warmly welcomed you aboard back in September, 2010 as #1 above was your very 1st post).

Does the saga continue here? http://www.polkaudio.com/forums/showthread.php?t=106512

[fbm211]

If we only knew then what we do now.

[jcandy]

I'm curious about what you did with your uncle's SDA-2B's, (especially with all that's transpired since several other members and I warmly welcomed you aboard back in September, 2010 as #1 above was your very 1st post).

Does the saga continue here? http://www.polkaudio.com/forums/showthread.php?t=106512
I advertised them on CL a few times, but nothing ever materialized. I was travelling alot during that time, and also coordinating the sale of many other items, so that probably cost me the sale. I turned down a few crazy low-ball offers. I'd rather hold on to them than give them away for $100. At this point they are still in my house, disconnected, but are promised to a friend of a friend -- presumably, as soon as he breaks the new to his wife :frown:

Before they are gone I am going to do an SL2000T versus RDO-194 HD comparison (I promised Face I would do this).

[jcandy]

I warmly welcomed you aboard back in September, 2010
I have said many times that I received some good tips when I first showed up. I do appreciate any and all honest help I've been given. The accusations of trolling that are continuously thrown my way (by a select few) are just plain weak; they're good examples of the pot calling the kettle black.

[inspiredsports]

I have said many times that I received some good tips when I first showed up. I do appreciate any and all honest help I've been given. The accusations of trolling that are continuously thrown my way (by a select few) are just plain weak; they're good examples of the pot calling the kettle black.

I've read the other forums where you starts threaded and the term troll was use in those cases also. Comment?

I've posted elsewhere that you show signs of high intelligence, like Rain Man with the matchsticks. But then you seem to cover your ears when the music is playing.

All work (measurement) and no play (listening) makes J a dull boy.

[On3s&Z3r0s]

I advertised them on CL a few times, but nothing ever materialized. I was travelling alot during that time, and also coordinating the sale of many other items, so that probably cost me the sale. I turned down a few crazy low-ball offers. I'd rather hold on to them than give them away for $100. At this point they are still in my house, disconnected, but are promised to a friend of a friend -- presumably, as soon as he breaks the new to his wife :frown:

Before they are gone I am going to do an SL2000T versus RDO-194 HD comparison (I promised Face I would do this).

Part 'em! Actually, I feel dirty just suggesting it, but if the tweeters are shot anyway... :wink:

[mossbacked]

I am trying to revive my uncle's SDA2Bs that suffer from (at least) the blown-tweeter problem. These speakers have great sentimental value: in fact, I drove them home myself in 1990, in a 1986 Honda Civic hatchback. I lost contact with him in the period 2002-2010, but recently he had a stroke :(. Now I am helping him to sell some items, and since I am a DIY audio fanatic, I offered to deal with the complete setup (also includes the high-end NAD pre-amp-tuner-cd from that era). The entire system was ridiculously expensive when purchased in August 1990 (seems like yesterday ...), and oddly enough, hasn't really been used for about 10 years. My uncle doesn't really like music!

Over the years, I believe two sets of replacement tweeters were ordered, but all tweeters he can locate are *dead*. I tested a random spare tweeter and this produced a roughly correct SPL, so I know there is a signal to the tweeters. The inner 6.5 driver is making NO sound, but I suspect this is because I don't have the SDA interconnect.

What should I do? Attempt to locate replacement tweeters, upgrade the crossover (I am comfortable with that), just sell them as-is, what

As I googled SDA2B my search landed here and I am wondering if they were for sale and can ship to 60952?